[1000mp] Very Hot Final Heatsinks

[Hans Remeeus]

Class-A uses a constant current. This constant current is important for 
a lower TX distortion. When you decrease the power output from 75 to 
e.g. 25 Watts this has to be absorbed by the heat sink. So the heatsink 
has two jobs: handle the constant (HIGH) current and handle the 
absorbtions of the 50 Watts in less power output. This is too much for 
the finals. When an amplifier is operated in Class A, it will be hottest 
at zero output power, because all of the DC power input will be 
converted to heat.

This is the main reason why I sold my Mark-V 200 and bought the Mark-V 
Field with 25 Watts Class-A, which is a very good power input for my 
linear amplifier Acom 2000A. It then gives 800 Watt power output, which 
in most situations is more than enough.

To be honest; who ever will notice that you are transmitting in Class-A 
instead of Class-AB...? IMHO Class-A is nice to have, but not need to have.

73,
Hans Remeeus (PA1HR)
http://www.remeeus.nl
Communication is about people, the rest is technology.




William Shadid schreef:
> Norm,
>
> Hans is correct. I long ago learned this with my Mark V -- leave the 
> power
> level at maximum on Class A. I note a higher temperature level in Class A
> but nothing like what I hear about on the reflectors. Up to now I had
> thought this to be a problem with selected radios -- but Hans' note 
> gets me
> to thinking that it is really a lack of understanding with the radio. 
> Yaesu
> should be more clear about this -- but they certainly do not have an 
> edge on
> things omitted from the manual!!
>
> I drive an older Drake L-7 with my Mark V and use the Class A selection
> simply to keep my drive power low. I do not use Class A when I run PSK.
> While I don't often run the amplifier, I can say that I note only 
> somewhat
> higher heat sink temperatures. The fins are far cooler than running older
> domestic, solid state radios such as an old Cubic Astro 103 with its 
> large
> rear heat sink. They are also much cooler than the single heat sink on my
> Ten-Tec Omni VI+ after a long operating session. If you are experiencing
> "scalding" temperatures at 75 watts output, Class A, I would say that 
> a call
> to Yaesu is in order.
>
> 73,
>
> -Bill, WA9MXQ
>